Male members of the marine snail species Solenosteira macrospira have it tough. Not only do they take on childcare duties, they also have to care for the offspring produced by other dads. To make matters worse, baby snails cannibalize their siblings while they're still embryos, a behavior the dads are helpless to prevent.

Adding insult to injury, the notoriously promiscuous female snails are far from the scene — off mating with as many as a dozen different males.

Writing in Wired, Tanya Lewis describes why males carry around egg capsules that contain only 25% of their own offspring:

After mating with their final male, females foist their paternal hodgepodge of eggs onto the shell of their unsuspecting mate, who carries the sack of babies around and keeps them moist and safe until they hatch one month later. Males often carry the egg capsules of multiple females, which almost entirely cover their shell (above).

The snail daddies weather their burdens despite losing weight for their pains...The species may be the only one known where males expend so much effort to care for offspring of which only a fraction are their own.

Why they do so is unclear, but one reason might be to impress the ladies with their childcare skills. Or, it might just be the price they pay for getting to mate.